The adrenergic neuron of the neonatal rat superior cervical ganglion will under certain culture conditions, express cholinergic characteristics. We have obtained some evidence that this capacity for transmitter "shift" is present only during certain stages of early development. We propose experiments designed to a) determine precisely the time during development when these neurons can be induced to express cholinergic properties, b) determine if dissociated adrenergic neurons cultured from mature rats may be induced to express cholinergic properties, and c) to determine which adrenergic properties may be retained as adrenergic neurons develop cholinergic mechanisms. In order to determine if the concept that target tissues may similarly influence neuronal development in a related, but quite different system, we propose to culture parasympathetic neurons and to study their basic anatomical and physiological properties in culture. We would present these neurons with both cholinergic and adrenergic targets in an effort to determine if adrenergic properties may be induced in these neurons during some stage in their development.